This invention relates in general to sorting and stacking devices and in particular to a new and useful stacker for letters and similar flat, flexible conveyed material.
In automatic letter distributing systems, the letters are transported singly on a conveyor track for the purpose of reading the place of destination automatically and subsequent sorting, and then they are assigned to a number of stack compartments over a compartment track with shunts corresponding to the postal zip codes, and they are stacked at such locations.
To produce the highest possible throughput, the letters run on the conveyor belt at the highest possible speed and at the shortest possible distances from one another. Under these circumstances, the problem of jamming arises with letters that are assigned to the same stack compartment, which is caused by the front edge of the following letter running into the rear edge of the preceding letter.
It is disclosed by German Patent Application Disclosure No. 33 27 865, for the case of letters resting vertically on their long edges during the stacking, how to have the bottom front edge of the letter run tangentially into a rotating spindle wheel, with the flank of the spindle wheel transporting the following parts of the letter, especially its rear area, toward the letters already stacked, so that the following letter reliably runs into the stack compartment along with the preceding letter.
However, the spindle wheel drive for each stack compartment is very involved and costly. For this reason, it has been attempted for precision distribution systems with a large number of stack compartments and low throughput to avoid the involved spindle wheel method by stacking the letters one on top of the other in the stack compartments, and by having the leading letter drop because of its weight and stiffness alone, using gravity, to such an extent that the following letter is pushed over the leading letter. In this case, however, difficulties arise when the letters, for example airmail letters, are very soft, and the sorting capacity is not to drop below a prescribed value.